Loans Held for Investment and Allowance for Credit Losses on Loans - Gross Loans Held for Investment by Year of Origination and Internally Assigned Credit Grades (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	$ 666,235
Fiscal year before current fiscal year	2,008,089
Two years before current fiscal year	997,214
Three years before current fiscal year	702,350
Four years before current fiscal year	365,300
Prior	785,344
Revolving Loans Amortized Cost Basis	969,808
Total Loans	6,494,340	$ 6,169,442
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	92,958
Fiscal year before current fiscal year	169,445
Two years before current fiscal year	149,681
Three years before current fiscal year	119,055
Four years before current fiscal year	60,441
Prior	157,001
Revolving Loans Amortized Cost Basis	36,038
Total Loans	784,619	684,739
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	53,454
Fiscal year before current fiscal year	130,071
Two years before current fiscal year	115,334
Three years before current fiscal year	94,782
Four years before current fiscal year	49,997
Prior	120,371
Revolving Loans Amortized Cost Basis	24,862
Total Loans	588,871
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	39,504
Fiscal year before current fiscal year	39,029
Two years before current fiscal year	33,297
Three years before current fiscal year	22,802
Four years before current fiscal year	9,986
Prior	35,244
Revolving Loans Amortized Cost Basis	10,657
Total Loans	190,519
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	42
Two years before current fiscal year	459
Three years before current fiscal year	601
Four years before current fiscal year	258
Prior	541
Revolving Loans Amortized Cost Basis	212
Total Loans	2,113
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	303
Two years before current fiscal year	591
Three years before current fiscal year	870
Four years before current fiscal year	200
Prior	845
Revolving Loans Amortized Cost Basis	307
Total Loans	3,116
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	53,455
Fiscal year before current fiscal year	311,216
Two years before current fiscal year	255,241
Three years before current fiscal year	170,159
Four years before current fiscal year	94,124
Prior	209,746
Revolving Loans Amortized Cost Basis	66,565
Total Loans	1,160,506	1,095,324
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	27,931
Fiscal year before current fiscal year	258,527
Two years before current fiscal year	208,346
Three years before current fiscal year	116,081
Four years before current fiscal year	51,072
Prior	118,840
Revolving Loans Amortized Cost Basis	37,306
Total Loans	818,103
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	18,461
Fiscal year before current fiscal year	52,282
Two years before current fiscal year	46,895
Three years before current fiscal year	50,872
Four years before current fiscal year	42,738
Prior	88,046
Revolving Loans Amortized Cost Basis	29,259
Total Loans	328,553
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	7,063
Three years before current fiscal year	3,206
Four years before current fiscal year	107
Prior	2,828
Total Loans	13,204
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	407
Four years before current fiscal year	207
Prior	32
Total Loans	646
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	68,612
Fiscal year before current fiscal year	197,654
Two years before current fiscal year	43,889
Three years before current fiscal year	55,198
Four years before current fiscal year	5,544
Prior	7,903
Revolving Loans Amortized Cost Basis	80,059
Total Loans	458,859	415,466
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	53,028
Fiscal year before current fiscal year	162,575
Two years before current fiscal year	39,428
Three years before current fiscal year	42,116
Four years before current fiscal year	3,719
Prior	6,572
Revolving Loans Amortized Cost Basis	35,506
Total Loans	342,944
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	14,386
Fiscal year before current fiscal year	32,079
Two years before current fiscal year	4,323
Three years before current fiscal year	13,028
Four years before current fiscal year	1,825
Prior	1,314
Revolving Loans Amortized Cost Basis	44,553
Total Loans	111,508
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,198
Fiscal year before current fiscal year	3,000
Two years before current fiscal year	105
Total Loans	4,303
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Two years before current fiscal year	33
Three years before current fiscal year	54
Prior	17
Total Loans	104
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	63,356
Fiscal year before current fiscal year	182,947
Two years before current fiscal year	4,995
Three years before current fiscal year	33
Prior	465
Revolving Loans Amortized Cost Basis	30,231
Total Loans	282,027	254,524
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	54,418
Fiscal year before current fiscal year	159,373
Two years before current fiscal year	4,522
Three years before current fiscal year	33
Prior	46
Revolving Loans Amortized Cost Basis	26,274
Total Loans	244,666
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	8,528
Fiscal year before current fiscal year	23,471
Two years before current fiscal year	473
Prior	419
Revolving Loans Amortized Cost Basis	3,957
Total Loans	36,848
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	410
Fiscal year before current fiscal year	103
Total Loans	513
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	95,638
Fiscal year before current fiscal year	298,179
Two years before current fiscal year	201,983
Three years before current fiscal year	120,142
Four years before current fiscal year	81,493
Prior	227,402
Revolving Loans Amortized Cost Basis	7,895
Total Loans	1,032,732	937,006
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	82,439
Fiscal year before current fiscal year	255,075
Two years before current fiscal year	172,583
Three years before current fiscal year	102,582
Four years before current fiscal year	65,952
Prior	174,331
Revolving Loans Amortized Cost Basis	7,895
Total Loans	860,857
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	11,906
Fiscal year before current fiscal year	41,467
Two years before current fiscal year	28,275
Three years before current fiscal year	15,303
Four years before current fiscal year	12,622
Prior	46,039
Total Loans	155,612
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,293
Fiscal year before current fiscal year	1,506
Two years before current fiscal year	886
Three years before current fiscal year	1,839
Four years before current fiscal year	1,936
Prior	4,688
Total Loans	12,148
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	131
Two years before current fiscal year	239
Three years before current fiscal year	418
Four years before current fiscal year	983
Prior	2,344
Total Loans	4,115
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	6,330
Fiscal year before current fiscal year	18,319
Two years before current fiscal year	15,922
Three years before current fiscal year	9,648
Four years before current fiscal year	6,738
Prior	18,679
Revolving Loans Amortized Cost Basis	85,207
Total Loans	160,843	161,018
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	5,357
Fiscal year before current fiscal year	15,974
Two years before current fiscal year	13,307
Three years before current fiscal year	7,665
Four years before current fiscal year	4,976
Prior	14,588
Revolving Loans Amortized Cost Basis	31,325
Total Loans	93,192
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	933
Fiscal year before current fiscal year	2,028
Two years before current fiscal year	2,342
Three years before current fiscal year	1,895
Four years before current fiscal year	1,470
Prior	3,044
Revolving Loans Amortized Cost Basis	52,937
Total Loans	64,649
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	40
Fiscal year before current fiscal year	304
Two years before current fiscal year	95
Three years before current fiscal year	88
Four years before current fiscal year	254
Prior	946
Revolving Loans Amortized Cost Basis	559
Total Loans	2,286
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	13
Two years before current fiscal year	178
Four years before current fiscal year	38
Prior	101
Revolving Loans Amortized Cost Basis	386
Total Loans	716
Real Estate [Member] | Farmland [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	21,425
Fiscal year before current fiscal year	64,860
Two years before current fiscal year	46,014
Three years before current fiscal year	47,473
Four years before current fiscal year	19,712
Prior	56,004
Revolving Loans Amortized Cost Basis	20,977
Total Loans	276,465	272,179
Real Estate [Member] | Farmland [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	15,574
Fiscal year before current fiscal year	44,160
Two years before current fiscal year	35,899
Three years before current fiscal year	23,593
Four years before current fiscal year	12,282
Prior	36,405
Revolving Loans Amortized Cost Basis	5,763
Total Loans	173,676
Real Estate [Member] | Farmland [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	4,505
Fiscal year before current fiscal year	16,679
Two years before current fiscal year	7,874
Three years before current fiscal year	22,007
Four years before current fiscal year	6,381
Prior	16,671
Revolving Loans Amortized Cost Basis	13,102
Total Loans	87,219
Real Estate [Member] | Farmland [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,346
Fiscal year before current fiscal year	2,896
Two years before current fiscal year	1,862
Three years before current fiscal year	1,873
Four years before current fiscal year	70
Prior	2,704
Revolving Loans Amortized Cost Basis	1,880
Total Loans	12,631
Real Estate [Member] | Farmland [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	1,125
Two years before current fiscal year	379
Four years before current fiscal year	979
Prior	224
Revolving Loans Amortized Cost Basis	232
Total Loans	2,939
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	97,428
Fiscal year before current fiscal year	375,136
Two years before current fiscal year	126,312
Three years before current fiscal year	98,264
Four years before current fiscal year	50,978
Prior	81,881
Revolving Loans Amortized Cost Basis	461,628
Total Loans	1,291,627	1,256,487
Commercial and Agricultural Non-Real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	77,553
Fiscal year before current fiscal year	296,814
Two years before current fiscal year	93,424
Three years before current fiscal year	75,665
Four years before current fiscal year	20,679
Prior	67,573
Revolving Loans Amortized Cost Basis	315,085
Total Loans	946,793
Commercial and Agricultural Non-Real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	17,955
Fiscal year before current fiscal year	75,007
Two years before current fiscal year	30,905
Three years before current fiscal year	20,516
Four years before current fiscal year	27,531
Prior	12,032
Revolving Loans Amortized Cost Basis	138,823
Total Loans	322,769
Commercial and Agricultural Non-Real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,562
Fiscal year before current fiscal year	2,516
Two years before current fiscal year	1,717
Three years before current fiscal year	1,136
Four years before current fiscal year	2,259
Prior	1,105
Revolving Loans Amortized Cost Basis	7,479
Total Loans	17,774
Commercial and Agricultural Non-Real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	358
Fiscal year before current fiscal year	799
Two years before current fiscal year	266
Three years before current fiscal year	947
Four years before current fiscal year	509
Prior	1,171
Revolving Loans Amortized Cost Basis	241
Total Loans	4,291
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	62,177
Fiscal year before current fiscal year	192,821
Two years before current fiscal year	74,228
Three years before current fiscal year	42,379
Four years before current fiscal year	16,017
Prior	8,152
Revolving Loans Amortized Cost Basis	23,716
Total Loans	419,490	413,370
Consumer Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	55,988
Fiscal year before current fiscal year	175,287
Two years before current fiscal year	67,276
Three years before current fiscal year	36,818
Four years before current fiscal year	13,972
Prior	5,867
Revolving Loans Amortized Cost Basis	21,964
Total Loans	377,172
Consumer Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	6,002
Fiscal year before current fiscal year	16,755
Two years before current fiscal year	6,569
Three years before current fiscal year	4,973
Four years before current fiscal year	1,806
Prior	2,179
Revolving Loans Amortized Cost Basis	1,749
Total Loans	40,033
Consumer Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	136
Fiscal year before current fiscal year	636
Two years before current fiscal year	299
Three years before current fiscal year	364
Four years before current fiscal year	129
Prior	103
Revolving Loans Amortized Cost Basis	3
Total Loans	1,670
Consumer Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	51
Fiscal year before current fiscal year	143
Two years before current fiscal year	84
Three years before current fiscal year	224
Four years before current fiscal year	110
Prior	3
Total Loans	615
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	99,198
Fiscal year before current fiscal year	136,667
Two years before current fiscal year	40,835
Three years before current fiscal year	13,732
Four years before current fiscal year	11,093
Prior	615
Revolving Loans Amortized Cost Basis	125,652
Total Loans	427,792	428,908
Oil and Gas [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	91,575
Fiscal year before current fiscal year	122,401
Two years before current fiscal year	32,400
Three years before current fiscal year	8,174
Four years before current fiscal year	1,174
Prior	110
Revolving Loans Amortized Cost Basis	93,578
Total Loans	349,412
Oil and Gas [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	7,623
Fiscal year before current fiscal year	8,352
Two years before current fiscal year	8,426
Three years before current fiscal year	5,558
Four years before current fiscal year	9,919
Prior	278
Revolving Loans Amortized Cost Basis	30,820
Total Loans	70,976
Oil and Gas [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	4,914
Two years before current fiscal year	9
Prior	227
Revolving Loans Amortized Cost Basis	1,185
Total Loans	6,335
Oil and Gas [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	1,000
Revolving Loans Amortized Cost Basis	69
Total Loans	1,069
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	5,658
Fiscal year before current fiscal year	60,845
Two years before current fiscal year	38,114
Three years before current fiscal year	26,267
Four years before current fiscal year	19,160
Prior	17,496
Revolving Loans Amortized Cost Basis	31,840
Total Loans	199,380	$ 250,421
Other Loans [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	5,658
Fiscal year before current fiscal year	60,549
Two years before current fiscal year	38,097
Three years before current fiscal year	26,158
Four years before current fiscal year	18,786
Prior	14,429
Revolving Loans Amortized Cost Basis	30,235
Total Loans	193,912
Other Loans [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	296
Four years before current fiscal year	65
Prior	2,933
Revolving Loans Amortized Cost Basis	471
Total Loans	3,765
Other Loans [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Four years before current fiscal year	140
Prior	82
Revolving Loans Amortized Cost Basis	1,052
Total Loans	1,274
Other Loans [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Two years before current fiscal year	17
Three years before current fiscal year	109
Four years before current fiscal year	169
Prior	52
Revolving Loans Amortized Cost Basis	82
Total Loans	$ 429